The defense attorney for a Somali man accused of being a pirate negotiator says he was unlawfully interrogated aboard a government airplane after requesting a lawyer.

Mohammad Saaili Shibin is charged with piracy, kidnapping and weapons charges for his role in the February hijacking of a yacht off the coast of Africa that left all four Americans onboard dead.

Prosecutors say Shibin never boarded the sailing vessel Quest, but he operated from land in Somalia to determine how much the hostages could be ransomed for. He is considered the highest-ranking pirate the United States has prosecuted.

Shibin's attorney James Broccoletti wrote in a court filing Tuesday that Shibin told FBI agents he didn't want to talk with them and that any statements he gave them should be suppressed. Shibin later changed his mind, said he understood his rights and made several incriminating statements.

Among other things, court documents say Shibin acknowledged negotiating the release of a German ship and receiving a $30,000 payment for it. Court documents also say Shibin told authorities he may have been approached to negotiate the release of the four Americans because he was unemployed at the time.

Broccoletti wants those statements and others suppressed.

"At the outset of the interrogation, Mr. Shibin told the agents that he did not want to speak to them and that he wanted to speak to an attorney. The government alleges that Mr.Shibin later 're-engaged the interviewing agents,' expressing his desire to answer questions without an attorney present," Broccoletti wrote.

Broccoletti contends prosecutors have to prove it was Shibin who initiated the additional discussion for it to be admissible in court.

"The government does not provide any insight as to what made Mr. Shibin change his mind about wanting an attorney present," he wrote.

The federal prosecutor's office said in an email that it has until the week of August 8 to respond to the filing but declined further comment.

"The statements Mr. Shibin made after his reengagement with the agents took place after a clear and unequivocal invocation of his right to counsel, without a break in custody, and before he was provided access to an attorney," Broccoletti wrote. "Such statements are presumed involuntary, even in the presence of a subsequent waiver of rights."

Shibin's trial is scheduled for Jan. 31. Eleven others in the case have already pleaded guilty to piracy and three others are facing murder charges. The eleven men who pleaded guilty agreed to help prosecutors in this case and possibly others in exchange for the possibility that their mandatory life sentences might be reduced.

The owners of the Quest, Jean and Scott Adam of Marina del Rey, Calif., along with friends Bob Riggle and Phyllis Macay of Seattle, were shot to death several days after being taken hostage several hundred miles south of Oman.

They were the first U.S. citizens killed in a wave of pirate attacks that have plagued the Gulf of Aden and the Indian Ocean in recent years, despite an international flotilla of warships that patrol the area.